1. Clean mushrooms with a damp cloth and remove their stems. Place in a glass dish, stem (gill) side up. With a paring knife cut a small x in the bottom of the mushroom cap. This will allow water to escape in the cooking process, providing a mouthful of flavor not water!

2. Grab a dish which will accommodate the mushrooms while they marinate. Drizzle the marinade over the cleaned mushrooms. Cover and marinate in the refrigerator for about 1 hour, turning mushrooms once.

3. In a saut pan over medium heat 2 Tbsp. olive oil. Once hot, add onions and stir. Reduce heat to low and cook until soft and translucent for about 10 minutes. {} Onions have lots of natural sugars and the higher heat at the beginning of the cooking process helps form a seal for the juices during the rest of the cooking process.{}Add salt and pepper to taste.

4. Prepare a hot fire in a charcoal grill or heat a gas grill or broiler. Away from the heat source, lightly coat the grill rack or broiler pan with cooking spray. Position the cooking rack 4 to 6 inches from the heat source. Grill or broil the mushrooms on medium heat, turning often, until tender about 4 minutes on each side. Baste with marinade to keep from drying out. Add slice of feta cheese and allow to melt slightly. {} Using tongs, transfer the mushrooms to a plate.

5. Prepare Kaiser rolls by splitting and spreading both sides with garlic mayonnaise. On top side of roll garnish with 1 slice of tomato and piece of bibb lettuce. Place each mushroom on the base side of roll and top with 1 tbsp. of caramelized onions. Serve immediately.